The conventional refrigeration units utilized for the separation of liquid hydrocarbons from natural gas utilizing the bubblecap system are well known in the art.
In the bubblecap prior art a chilled glycol was injected at the top of a separation tower and allowed to filter down through the tower. The natural gas having the liquids therein to be separated was injected from the bottom of the distilling tower to allow the chilled glycol to contact the liquid gases to be separated. Trays were provided along the walls of the tower for increased surface area and to create condensation points along the length of the tower. Thus, in the prior art the glycol coolant was in direct contact with the gases to be separated.
In this prior art the liquid hydrocarbons to be removed and the glycol coolants settled to the bottom of the tower in a liquid form and the natural gas was evacuated from the top of the tower.
Also in this prior art, deicers such as methanol were injected along the sides of the tower at various ports to prevent the formation of ice along the length of the tower and at the top of the tower where the bubble caps are located. The glycol, methanol and liquid hydrocarbons which were collected at the bottom of the towers were then separated from the hydrocarbons, but only about 50 percent of the glycol was returned in the separation process to the glycol unit for recirculation in the process. Thus, in the bubblecap process about 50 percent of the glycol is lost in the liquid hydrocarbons and must be added as makeup glycol to keep the bubblecap system in operation.
Further, the hydrocarbons were required to have the other 50 percent of the glycol refined out of them prior to further distillation of the liquid hydrocarbons.
Also in the bubble cap process methanol was injected up and down the walls of the tower to prevent ice formation which resulted in a relatively high consumption of methyl alcohol as a deicer in the bubblecap system of the prior art.
Also, even though a deicer was added in the form of methanol, occasionally ice does form in the prior art systems and since they rely on a mechanical bubble cap at the top of the tower to open and close there has been problems with the caps icing shut which closes down the whole system until the ice could be cleared.
In the prior art so much re-refining and separating is required to remove the glycol and methanol from the liquid hydrocarbon that it utitlized excessive energy in its operation.
Also, the prior art is relatively expensive because of the size of the equipment necessary to be utilized and its mechanical complexity. Further, because of its large size it was very difficult to set up and it required a certain amount of field work to bring the unit on stream when it was installed.
Also in the bubblecap system of the prior art the minimum efficiency for the operation of these type units was a million cubic feet of gas per day, and while they may be operated below that limit of volume, at that point they are being run very inefficiently.
Further the prior art patents require that the systems be operated at a positive pressure of at least 2 pounds per square inch.
Further, in the prior art the methyl alcohol was injected at the condensation point and, therefore, had to be injected in larger quantities because it was being injected at the point of ice formation and required larger quantities in order to have the beneficial effect of the methanol present at the formation of the ice crystals, which were already in the process of forming at the time of injection.